The present invention relates to a tubeless radial tire for heavy duty use, and more particularly to an improvement in the profile of a carcass in bead regions which is capable of preventing bead toes from being lifted from the bead seat of its rim while the tire is mounted thereon.
Recently, tubeless radial tires have been widely used for heavy duty use, e.g. truck and bus use.
As the tire pressure and tire load of such a tubeless tire is fairly large in comparison with those in passenger car tires, the engaging force and air-seal between the tire bead portions and the rim bead seats must be higher. However, when such a heavy duty tire is reused by retreading, the bead toe (a) is, as shown in FIG. 8, often lifted from the bead seat (b) of the rim (j) to form a gap (f). The gap (f) leaks the air during initial inflation, which makes it difficult to inflate the retreaded tire. Further, the gap decreases the engaging force between the tire bead portions and the rim bead seats in the inflated state of the retreaded tire.
An examination about the toe lift was made using Computer Tomography, and it was found that:
1) such a toe lift existed before the worn tire is retread, and this toe lift remains after the tire has been retreaded, and PA1 2) even in a new tire which is mounted on its regular rim and inflated to a high inner pressure, a toe lift occurred, and the amount thereof is almost the same value as that in the worn tire state, PA1 3) the amount of bead toe lift (F) in a worn tire state or the amount of bead toe lift in a new tire state is in direct proportion to the amount of bead toe lift (f) in a retreaded tire state, as shown in FIG. 6, and PA1 4) the durability of bead portions of a retreaded tire is in inverse proportion to the amount of bead toe lift (f), as shown in FIG. 7. PA1 a pair of symmetrically shaped bead cores disposed on in each of the bead portions, PA1 a radial carcass having cords extending between the bead portions and turned up around the bead cores, and PA1 a belt layer disposed radially outside the carcass and inside a tread, PA1 in each bead portion, the carcass provided with a profile such that the inclination thereof at a point (P) located at the same axial distance as the geometric center of the bead core from the tire equator is not more than 53 degrees with respect to the axial direction of the tire when the tire is mounted on the regular rim and inflated to a pressure of 0.5 kgf/sq.cm.
The main cause for a toe lift is a radially outward displacement of the carcass cords (c) caused by inflation to a high inner pressure, which displacement pulls up the surrounding bead rubber, and the bead toe (a) is lifted.
Further, the bead rubber is subjected to deformation repeatedly during running under heavy loads with generating heat, and such a toe lift turns into a permanent deformation of rubber in the worn tire state.
Further, it was confirmed that the above-mentioned problems in the retreaded tire can be solved by preventing bead toes in a new tire state from being lifted from rim bead seats or preventing the bead rubber from being pulled radially outwardly by the carcass.